National SW-3 question
 

Michael Black wrote:
Bill M ) writes:

I'm toying with the idea of building a SW-3 clone. One thing has me
puzzled, though, and thats the 700H choke in the audio coupling circuit.
Any ideas how to duplicate that or a simple workaround? Does anyone
know the DC resistance of the original unit? I have no idea why such a
value was used - any explanation?

TIA,
Bill


IN the early seventies, like 1971 or 72 I'd say, CQ ran an article
by Bill Orr about making your own National regen receiver. My
first thought was that it was an SW-3, but I can't remember. But
if someone can dig that article up easily (it was on the cover),
it might provide some insight.

Michael

I'd like to see that if anyone has it.

-Bill

Hi,

This Bill Orr article may be what you are looking for -


http://www.thecompendium.net/radio/SW-3/SW3maginfo.pdf


Incidently, the large choke in the audio coupling circuit is
there to obtain as high an AC gain as possible at the expense of
a relatively low DC voltage drop. The fact that the grid leak and
coupling capacitor are all part of the same assembly suggests
that National used the same arrangement is several designs.


Cheers - Joe

Joe McElvenney wrote:

Hi,

This Bill Orr article may be what you are looking for -


http://www.thecompendium.net/radio/SW-3/SW3maginfo.pdf


Incidently, the large choke in the audio coupling circuit is
there to obtain as high an AC gain as possible at the expense of
a relatively low DC voltage drop. The fact that the grid leak and
coupling capacitor are all part of the same assembly suggests
that National used the same arrangement is several designs.


Cheers - Joe

Great! Thank you very much.

-Bill

"Bill M" wrote in message
...
Joe McElvenney wrote:

Hi,

This Bill Orr article may be what you are looking for -
http://www.thecompendium.net/radio/SW-3/SW3maginfo.pdf
Incidently, the large choke in the audio coupling circuit is there to
obtain as high an AC gain as possible at the expense of a relatively low
DC voltage drop. The fact that the grid leak and coupling capacitor are
all part of the same assembly suggests that National used the same
arrangement is several designs.
Cheers - Joe

Great! Thank you very much.

-Bill

Could you use one winding of say an audio output transformer; the primary,
with nothing connected to the secondary?
The primary winding becoming a high inductance choke!
Found that out the hard way one time!
The speaker became disconnected; the primary was in the plate circuit of a
6V6, audio output pentode.
No sound, turned up volume, naturally, like you would!
Result sparks during peaks in the music from the plate pin of the tube
socket to a nearby ground/chassis wire or summat. Ah yes, high inductive
reactance, some audio power and induced voltage.
Lucky didn't burn out the insulated primary of the audio transformer!